Developer Overkill has added microtransactions to Payday 2, after stating, on multiple occasions, that it wouldn't. They're part of the Black Market update, which allows players to crack open safes to claim random loot drops. You'll need to microtransact £1.60 of real money, to buy consumable drills that will be able to bust them open.

People aren't too happy about this change. Here's a big Reddit thread entitled "Fuck you overkill", and here's the Steam page, which is in the process of being drowned in negative reviews.